limbic system

limbic system

composed of functionally and anatomically interconnected nuclei and cortical structures that are located in the telencephalon and diencephalon

functions of limbic system

1. regulate autonomic and endocrine functions - particularly in response to emotional stimuli

2. set level of arousal and are involved in motivation and reinforcing behaviors that are critical for particular types of memory

cingulate lobe

parahippocampal lobe

hippocampus

amygdala

orbital and medial prefrontal cortex

limbic system structures:

parahippocampal gyrus

cingulate gyrus is continuous with BLANK BLANK

amygdala

anterior cingulate lobe

ventromedial prefrontal cortex

anterior temporal lobe

involved in emotional experiences

hippocampus

posterior cingulate lobe

parahippocampal gyrus

play a role in learning, memory and spatial orientation

hippocampus

located in the temporal lobe and surrounded by the parahippocampal gyrus; located lateral to the inferior horn of the lateral ventricle

dentate gyrus

hippocampus proper

subiculum

3 layers of the hippocampus:

subiculum

transition area that connects the hippocampus proper to the entorhinal cortex

entorhinal cortex

rostral portion of the parahippocampal gyrus

• functions as a widespread network hub for memory, navigation, and the perception of time; the main interface between the hippocampus and neocortex; important area for memory consolidation due to extensive projection to this area from all association areas of the cortex and the reciprocal projections from the entohinal cortex back to these areas

fornix

2-way street carrying axons in and out of the hippocampus; provides link between hippocampus and hypothalamus to produce emotional responses to various stmuli

anterior commissure

interhemispheric bundle of axons that course between right and left temporal lobe

fimbria

caudal edge of the hippocampus

crus

leaves hippocampus; course inferior to corpus callosum

body

left and right crura come together to form this portion of the fornix

postcommissural portion

precommissural portion

fornix splits into two at the anterior commissure

postcommissural portion

caudal to anterior commissure; terminate in mammaliary bodies

precommissural portion

rostral to anterior commissure; terminate in septum and ventral striatum

CA1

CA2

CA3

CA4

4 regions of hippocampus proper:

CA1

continous with subiculum, neurons carry the output of the hippocampus to the entorhinal cortex

CA4

surrounded by the dentate gyrus

association areas

olfactory bulb

entohinal cortex receives afferents from:

perforant pathway

mossy fiber pathway

schaffer collateral pathway

three pathways that make up the tri-synpatic intrinsic pathway

perforant pathway

entohinal cortex projects to dentate gyrus

mossy fiber pathway

dentate gyrus projects to CA3 region of the hippocampus proper

schaffer collateral pathway

CA3 pyramidial cells project to CA1 pyramidial cell

place cells

some cells in the hippocampus have strong firing rate when freely moving animals occupy a specific place in a defined space

grid cells

in the entohinal cells that also map points in a defined space over specific distances; thus they provide measurement information on the area which Place Cells use to couple environmental cues with distance and direction

posterior hippocampus

important for remembering spatial information

anterior nucleus of the thalamus

mammillary bodies of hypothalamus

septum

ventral striatum

neurons in the subiculum/entorhinal cortex project to the following areas via the fornix

declarative memory

memory of facts and events, and refers to those memories that can be consiously recalled; requires intact medial temporal lobe (hippocampus)

semantic and episodic memories

declarative memory can be divided into two categories

semantic memories

focused on general knowledge about the world and includes facts, concepts and ideas

episodic memory

involves recollection of particular life experiences

anterograde amnesia

difficulty forming new explicit memories

association areas

entorhinal

hippocampus

mammillary bodies

fornix

hippocampal-diencephalic memory system for episodic memory generation:

BLANK BLANK of the cortex carry information such as spatial or object which is brought individually into the parahippocampal and perirhinal cortices.  This information is sent to the BLANK cortex  where it is integrated into an episode (apple pie and grandma’s house at Thanksgiving).  This information is sent to the BLANK where it is temporarily stored and further processed.  This is then sent to the BLANK BLANK of the hypothalamus via the BLANK.  From the MBs it is sent to the anterior nucleus of the thalamus which projects to the prefrontal cortex where it is permanently stored.

amygdala

links cortical processing to the hypothalamus and other subcortical brain structures important for emotional behavior

sensory areas (auditory, somatic, olfactory)

visual association area

brainstem

hypothalamus

septal nuclei

thalamus

major inputs to amygdala:

lateral hypothalamus

output of amygdala; causes sympathetic activation (pupils dilate, heart rate increases)

locus ceruleus

output of amydgala; causes activation of epinephrine — leads to arousal and increased vigilance

PVN

output of amygdala; causes the release of ACTH which leads to corticoid release and the generation of the stress response

kluver-bucy syndrome

lesions in amygdala lead to monkeys being tame and FEARLESS; produced blunted emotions

microstimulation of the amygdala

produces feelings of fear and apprehension

urbach-wiethe disease

isolated lesions in the amygdala, leaves calcifications in the amygdala bilaterally - impair patients from learning how to discern emotions in facial expressions

• amygdala is activated differentially by emotional facial expressions; also responds to emotionally arousing stimuli

fear conditioning

process in which a neutral stimulus is paired with an averisve stimulus so that the conditioned stimulus comes to predict an aversive outcome, elicitng fear behaviors even in the absence of the unconditioned stimulus

skin conductance response

quantitative psychophysiological measure that has been correlated with emotional arousal

flash-bulb memories

highly detailed, exceptonally vivid snapshot of the moment and circumstances in which a piece of suprising and consequential news was heard

sympathetic

HPA

amygdala

Emotionally arousing events activate the BLANK nervous system and the BLANK axis, resulting in the release of epinephrine and glucocorticoids. In addition to mediating aspects of the “flight-or-fight” response, these hormones have now been shown to improve emotional memory, and that the BLANK is critical for this process.

post-traumatic stress disorder

Occurs following a traumatic stressor such as robbery, combat that elicits feelings of fear, horror or helplessness to prevent bodily injury or threat of death.

basic circuit for eliciting a fear response

Think of being alone in your home and all of a sudden you hear an unfamiliar noise.  Initially this is perceived of as an auditory danger signal.  It is perceived by the medial geniculate nucleus of the thalamus which projects to the auditoy cortex and directly to the amygdala. 

As we saw on the previous slide, this could then initiate a cascade of behavioral, autonomic and stress responses.  Why doesn’t this always happen.  Well remember the projection from medial geniculate to the auditory cortex?  This is where the sound is interpreted.  It might be identified as something benign such as your cat jumping off a shelf, or your washing machine switching to another cycle, or your alarm clock going off because you forgot to turn it off earlier. 

Once the noise is perceived of as non-threatening, there are projections to the amygdala that inhibit the output to these autonomic and stress centers.